A Theoretical Framework for Inference and Learning in Predictive Coding
Networks
- URL: http://arxiv.org/abs/2207.12316v1
- Date: Thu, 21 Jul 2022 04:17:55 GMT
- Title: A Theoretical Framework for Inference and Learning in Predictive Coding
Networks
- Authors: Beren Millidge, Yuhang Song, Tommaso Salvatori, Thomas Lukasiewicz,
Rafal Bogacz
- Abstract summary: Predictive coding (PC) is an influential theory in computational neuroscience.
We provide a comprehensive theoretical analysis of the properties of PCNs trained with prospective configuration.
- Score: 41.58529335439799
- License: http://arxiv.org/licenses/nonexclusive-distrib/1.0/
- Abstract: Predictive coding (PC) is an influential theory in computational
neuroscience, which argues that the cortex forms unsupervised world models by
implementing a hierarchical process of prediction error minimization. PC
networks (PCNs) are trained in two phases. First, neural activities are updated
to optimize the network's response to external stimuli. Second, synaptic
weights are updated to consolidate this change in activity -- an algorithm
called \emph{prospective configuration}. While previous work has shown how in
various limits, PCNs can be found to approximate backpropagation (BP), recent
work has demonstrated that PCNs operating in this standard regime, which does
not approximate BP, nevertheless obtain competitive training and generalization
performance to BP-trained networks while outperforming them on tasks such as
online, few-shot, and continual learning, where brains are known to excel.
Despite this promising empirical performance, little is understood
theoretically about the properties and dynamics of PCNs in this regime. In this
paper, we provide a comprehensive theoretical analysis of the properties of
PCNs trained with prospective configuration. We first derive analytical results
concerning the inference equilibrium for PCNs and a previously unknown close
connection relationship to target propagation (TP). Secondly, we provide a
theoretical analysis of learning in PCNs as a variant of generalized
expectation-maximization and use that to prove the convergence of PCNs to
critical points of the BP loss function, thus showing that deep PCNs can, in
theory, achieve the same generalization performance as BP, while maintaining
their unique advantages.
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